Protection apparatus



' Aug. 21, 1945.

H. w. HOFFMAN ET AL PROTECTION APPARATUS Filed May 7, 1943 4Sheets-Sheet 1 ew w z \Ot Q W W a FHM z m H T h mm MH. A x f NEIL: #MWH1 a U 1 M 2 1945 H. w. HOFFMAN ET AL 2,383,313

PROTECTION APPARATUS Filed May 7, 1345 4 Sheets-Sheet 2 m m w m m I N aa a 3 a wig 0/ 4 w u Aug; 21, 1945. H. w. HOFFMAN ET AL PROTECTIONAPPARATUS Filed May 7, 1943 4 Sheets-Sheet 3 LB WM, 4 1 9 W A'r-roBNE-Y:

H. w. HOFFMAN ETAL 2,383,313

PROTECTION APPARATUS Filed May 7, 1945 4 Sheets-Sheet 4 Patented Aug.21, 1945 PROTECTION .APPARATUS 7 Harry William Hoii'man,

Helmet, Minneapolis, Minn eral Cartridge Corporation,

Anoka, and Grover 11..

., assignors to Feed Minneapolis, Minn.,

a corporation of Minnesota. Application May 7, 1943, Serial No. 486,026

17 Claims.

This invention relates to inspection and gauging apparatus and moreparticularly to photoelectrically operated systems for controlling theoperation of mechanical shaping presses such as draw, punch, shear andforming presses and the like. The invention is adapted to be used onfast or slow speed single operation or multiple operation presses, thelatter being of the type wherein the work undergoing formation issubjected to several operations successively or several work units aretreated simultaneously.

Each cycle of operation of such press includes movement of the work intoplace by suitable feed mechanisms, work performing operation of thepress with resultant cutting, swaging, drawing or other work operation,opening of the press, ejection of the work, and transl'elral orthe Walkaway from the machine or to another work position in the machine. Inrapid action presses, such forming operations may take place at the rateof 50 to 60 complete cycles per minute. Only a, very small fraction of asecond is consumed by the actual work operation and an equally smallinterval is available for moving the work into and ejecting it from thework station.

During the operation of punching, drawing. shearing, shaping and thelike operations, the work part undergoing treatment not infrequentlybecomes misaligned in respect to the die, shear,

. punch or other work tool, and when this occurs great damage may bedone to the work tool. An operator stationed at the machine is sometimesable to stop the machine in time, after discovering the malfunctioningof the machine, but in the case of rapid operations particularly, theoperator is not usually quick enough to stop the machine and the damageis done before the machine can be halted. This is no reflection on theoperator because to prevent the damage, he must be on the alert hourafter hour, poised under tension for a very quick movement of thestopping controls, awaiting for an emergency that may come the nextinstant or not for many hours. Fatigue sets in after a short period withth inevitable results that no operator however conscientious is able toguard such a machine adequately.

It is an object of the present invention to provide a photoelectricapparatus for protecting the work performing machinery.

It is a further object of the invention to provide an improvedphotoelectric control and operational circuits, and improved amplifyingcircuits.

It is also an object of the invention to provide an improved method andapparatus for activating and inactivating the photoelectric controlapparatus during certain cycles of the work.

It is another object of the invention to provide an improved testing andinspection method wherein the part undergoing consideration is inspectedbefore and after work is done, and to provide improved control apparatusfor shifting the period of inspection in respect to the cyclic operationof the machine on which the work is processed.

Other and further objects of the invention include the provision ofrugged, simple photoelectric circuits and apparatus, capable of use byinexperienced personnel, and provision of improved light source andphotoelectric devices, circuits and controls in testing, inspecting andcontrol apparatus.

Further objects of the invention include those inherent in and impliedby the methods and apparatus herein illustrated, described and claimed.

The invention is illustrated with respect to the drawings in whichFigure l is a fragmentary plan view of a multiple draw pressillustrating on mode of installing the invention.

Figure 2 is a fragmentary sectional view of the apparatus of Figure 1.The portion of Figure 2 at the level of the photocell and light sourceis taken along the straight sectional line a-k of Figure 1, whereas theportion of Figure 2 below the line 22 is taken e, ,f, g, h, 1', k inorder to present certain'of the mechanical details in the mostillustrative manner.

Figure 3 is a wirin diagram of the responsive and control circuitsutilized.

Figure 4 is a diagrammatic illustration of the cycle of operation.

Figures 5, 6 and 7 are views of a desirable cam utilizable in theinvention.

The invention is illustrated with reference to a multiple stage drawpress which may be used for forming mechanical parts in a plurality ofsuccessive operations. While the invention has particular usefulness forprotection. of such presses, it is to be understood that it is alsowidely applicable to other forms of work performing machinery, andtherefore the specific apparatus herein illustrated is not to be takenas a limitation upon the invention, although features of novelty thereofare claimed.

In Figure 1, there is illustrated a press, which may for example be ofthe general type illustrated in Patent 1,602,334 to Candee. Where apress of this type is used for shell or bullet formalong the lines a, b,c, d,

transversely at spaced intervals to receive and".

support the die blocks I, 2 and 3 and there ac- I cordingly remain lands8, 9, l and II, the upper surfaces of which are even with the top of thedie blocks (Figure 2). The die blocks may be fastened to the die blocksupport in any suitable manner, not illustrated.

Each of the die blocks I, 2 and 3 is provided with a hardened steel diel3 of suitable design for shaping the work in an appropriate fashion. Asusually constructed, the hardened steel die I3 is pressed into the dieblock from the lower side. as shown in Figure 2, until the shoulder I4of the hardened steel die engages a similar shoulder on the die block.In some instances, an ejector pin 16 may be provided in the hardenedsteel die for ejecting the work after the shaping or forming stroke hasbeen completed, although in other instances, as in drawing, punching,shearing and many similar operations, the work may hang upon the worktool sufficiently to be withdrawn from the press without the use of anyejecting apparatus. The specific tool shape, and the work feed, transferand ejecting means, if used, constitute no part of the presentinvention.

In the illustrated multiple stage draw press, there is provided atransfer mechanism for moving the work successively from the position ofdie I to die 2 and thence to die 3, and so on through the series untilthe work is completed and ejected. For accomplishing this purpose, thereare provided transfer bars, generally designated 20, which are held inspaced relationship, as shown in Figures 1 and 2, by any suitablespacing blocks (not illustrated). The transfer bars are arranged foroscillatory motion back and forth in the direction of the double arrow2! (Figure l), in timed relationship to the cyclic work motion of thepress.

Upon the transfer bars 20, there are mounted opposed pairs of fingers23-24, 25-26 and 21-28. Each of the fingers is mounted for pivotingabout a vertical axis. The opposed fingers 23-24, for example, arearranged to be pressed towards each other by means of compressionsprings 35 and 36, and the ends of fingers 23 and 24 are shaped toengage the work before and after the working operation at the particularstage in question.

Thus, in a usual sequence of operation, transfer bars'2ll may move tothe left, carrying with them all of the pairs of opposed fingersattached thereto. This movement usually occurs while the work is beingaccomplished, i. e., while the punching, shearing or drawing operationis being accomplished by the descending tools of the press head, and thefingers stop at a position so that each pair of fingers will resideconcentrically with one of the dies. Then after the press head haslifted, the work is either drawn upward or ejected in between thefingers and is there gripped as shown in Figure 2. Thus, fingers 23-24will be above the die opening of die block I; fingers 25-26 will beabove the openings of die block 2, and fingers 21-28 above the openingof die block 3. Then as the press head lifts, the work is either drawnoutwardly by the die tool or is ejected and the work is forced betweenthe finger bars and is gripped. Then while the press head is in anelevated position, the transfer bars 20-20 move to the right, as shownin Figure l, for a distance equal to the distance between the centerlines of the die blocks and so as the press again descends, the work ofeach stage has been moved to the right, in Figure l, and is forced intothe die of the next stage for further shaping, punching, drawing, etc.

In such a scheme of operations, everything will proceed smoothly untilperchance one of the work pieces happens to be misplaced crosswise ofthe die or some other derangement takes place, then as the die descends,it impinges upon the out-of-place work and great damage is done to thedie frequently causing a complete breakage of the die in the die block.

In order to prevent this unwanted action, there are provided one or morephotoelectric testing stations, one such station being provided at eachcritical or troublesome stage of the operation, or if the press performsonly one operation, one photoelectric inspection device is provided atthe single work performing place. Thus, in Figures 1 and 2, there areillustrated two photoelectric viewing devices and light sources and asthese may be identical, only one need be described. These include alight source, generally designated 40, mounted upon a vertical post 42,having an apertured upper head 43 of such a size so as conveniently toreceive the mounting and focusing nipple 44 of the light source. Thepost is conveniently bolted to the land 8 and is milled off at the topso as to present opposed fiat faces, normal to the center-line throughthe light source and the work (line (Yr-k of Figure 1).

Referring to Figure 2, it will be observed that the mounting andfocusing nipple 44 has a slide or press fitin the apertured upper end 43of the support rod 42, and may be held by a set screw, if desired. Thenipple 44 is enlarged at the light carrying end and is provided withthreads 45 which receive an internally threaded housing 46, the rearportion of which is likewise threaded to receive the lamp mountingsocket and conduit 41. For purposes of adjustment, the housing 46 isthreaded upon the nipple 44 to any degree desired and locked in place bymeans of a lock nut 48, and the lamp position may also be varied byscrewing the lamp mounting conduit 41 into the housing 46 by a variableamount. The conduit 41 may be locked in any position by means of a setscrew 49. Within the nipple 44, there are a plurality of light screeningrings 50 and a condensing lens 56. Upon the outer portion of housing 46,there are provided a plurality of heat radiating fins 53 for dissipatingthe heat of the lamp 55. The lamp 55 ma conveniently be of theautomotive type and it may be noted that the life is increased severalfold by providing for radiation and dissipation of the heat by means ofthe radiating fins 53.

The light source 40, thus projects a narrow beam of light A directlyacross the position normally assumed by the work piece W either as it isready to be forced into the die l3 or immediately after the ejection ofthe work from the die.

' It will be appreciated that in this position, the

work W is gripped by the fingers 23-24, 25-26 or 21-28 (depending uponthe particular stage of operation), and that the upper level of thefinger bars is even with the top of the transfer bars 23, so that aportion of the work W projects in a position to intercept the beam oflight A, provided the work is in correct position.

Diagonally opposite the light 44, there is positioned a photoelectriccell housing, enerally designated 60, which is mounted in a mannersimilar to the mounting of the light source 40 upon a post 6|, having abeveled and apertured top 52. Post GI may conveniently be bolted to land9. The photoelectric cell housing 64 is screw threaded at 65 forattachingto a nipple 63, the latter being slip fitted or' pressed intothe aperture 62 and optionally held in post 6| by a set screw, notillustrated. The housing 64 is threaded at its rear portion to receivesocket and conduit member 66. If desired, the nipple 63 may be providedwith a concentrating lens 68 or merely a glass window to exclude dustand grime. Upon the socket base 66, there is mounted a photocell 69,

and the interior of the entire photocell mountingis finished a dullblack so as to obviate deleterious effects of stray light.

Referring to Figure 4, there is diagrammaticall illustrated a completecycle of operation of the press. The eccentric, cam or crank shaft foroperating the press is illustrated at Ill, and the work ejector cam(When used) is showri at 85. In normal cyclic operations, the shafts Iand 85 operated continously and the various phases of each working cyclemay thus be illustrated by the wave diagrams shown in these figures. Inthe illustration herein given, arrangement is made for photoelectricallyinspecting the work just preceding and just after the work operation,these inspection periods being illustrated by periods I3 and 80 of thecycle. These timing periods may be achieved as hereinafter morefullydescribed by the use of a switch operated by a cam on a reciprocating orrotating part of the press. At the point of maximum elevation of thepress head illustrated at Start of cycle, the transfer bars fill-21) arein the course of moving from left to right. This transfer bar movementis initiated at II and continues to I I at which time the press head hasalready begun its downward stroke. The movement of the transfer bar tothe right serves to carry the work at each stage to the next stage insuccession (or in a single stage press, feeds the work to the machine),and at point I2 the work in normal operation has been brought to aproper position over the die opening inquestion. In order to determinewhether this proper action has or has not occurred, a detection periodis provided, during which the photoelectric inspection takes place, thisperiod being illustrated by bracket I3. During the detection period, thepress head is moving downward and if the work is not properlypositioned, the press is stopped before the beginning of the work strokeat point M. Stopping is accomplished by suitable electrical controlswhich are responsive to the photocell impulse, all as hereinafterdescribed.

Assuming that the work is properly in place, the press head descends,engaging the work at 74, forcing itinto the die from I4 to the low point15. Thereupon the press head again begins its upward movement until atpoint 16, the tool is normally free of work. During the work stroke fromI to IS, the transfer bars 20-20 move to the left, this movement beingstartedat I8and completed at I8, so as to be ready to receive the workas it is withdrawn or ejected from the die. Normally, the transfer baris in position to receive the work, and the work is withdrawn or ejectedupwardly in between fingers 23--2| (or 25-26, ill-28, as the case maybe), to the position shown in Figure 2, in which position the workintercepts the light beam A. A second inspection period, as indicated atthe bracket 80, is provided in order to a die I.

curred and that the work is in position between the fingers to be movedby the transfer bar to the next station. Should the work not be inproper condition at this point, the machine is stopped, as hereinafterdescribed.

The motion of the ejector pin is accomplished by an elevator cam whichis schematically illustrated at 85 in Figure 4, the action of this cambeing initiated at or shortly after the Dress head has been withdrawnfrom the work, point 16. The elevator cam begins its work at 11,completes its work at 19 and again descends to the lowered position, asindicated at 8|, shortly before the press head has reached the end ofits cycle of operation indicated at 82. The detection period ispreferably timed so as to begin slightly before the elevator cam hasreached its ultimate point 19 and continues after the elevator cam hasbegun to descend so that the press will be stopped in the event the workadheres to the ejector pin and be pulled back down towards the die (andhence out of the grip of the transfer bar fingers).

The detection periods, during which the photoelectric inspectionapparatus is effective to cause stopping of the press in the event ofderangement of the work, is preferably determined by means of a camoperated switch operated in conjunction with the press. The verticallyreciprocating press head of the press serves very well.

timing of the detection periods by means of a fixed cam solidly fastenedto the press head or other reciprocating part of the machine, the cambeing arranged to operate upon asuitable switch on the frame of themachine. In other installations, it is desirable to provide anoscillatory cam is interposed by the work. Since the work units W arenormally moved in working and transfer to and from the die blockposition, it follows that the lamp light shines upon the cellperiodically even during proper operation. In order that the photocellimpulses so produced may not elfect a false stoppage of the machine, thephotocell action is obviated except during the inspection periods, thisbeing accomplished by the machine operated cam, as hereinafterdescribed.

In some schemes of operation, it is desirable, for example, to inspectthe work as it is ready to be worked upon at die block I and immediatelyafter it has been, ejected from die block I. The second inspection atdie I serves to protect die 2, in case the work is tipped over by theaction of the transfer bars or, for other reasons, does assume aposition propitious for transfer, while at Similarly, the inspectionbefore and after working atdie block 3 serves as an inspection for dies2 and 3 and the next succeeding die in the press as may in someinstances be provided. Thus, the first inspection at die 3 serves toprotect die 2, in the event the work stuck in die 2 or was ejectedbeyond the transfer bars. Anyab sence of work during the firstinspection at die 3 thus serves to stop the press and protect the dies;

It is expedient in some installations to accomplish the wire 90.

being made either before, or before and after the work is acted upon.

Referring to Figure 3, there is illustrated amplifying and controlcircuits for utilizing the very lowenergy output of the photocellsduring the effective inspection periods and for obviating such actionduring non-inspection periods. Photoelectric cell 69 (at die block I)and photocell 69' (at die block 3) together with any other photoelectriccells 89", which may be utilized in the control apparatus of one machineare connected in parallel relation to ground connection 90 and to a gridconnection ill of a grid controlled thermionic amplifier 92. Theamplifier 92 may be of the type including only a cathode grid and plate,but is preferably of the five element type including cathode 93, (whichis indirectly heated by an alternating current filament 94), a controlgrid 95, supplemental grid 96, screen grid 91 and plate 90. The screengrid 91 is connected to the cathode 93 by means of connection I and thecontrol grid 95 is connected to the photoelectric cells by wire 9!. Theentire tube is protected by a shield IOI, which is grounded at I02. Thesupplemental grid 96 and plate 98 are connected by means of lead wireI03 to tap I04 on a potentiometer resistor, generally designated I05,which is supplied with direct current at approximately 300 volts D. C.from the power pack I08. The power pack I06 is energized fromalternating current supply lines I0'I of any suitable voltage throughfuses I08 and control switch I09 through lines I I0 and III and throughpower pack fuse H2 and switch H3. Line III is grounded as indicated atII4 and one terminal of the D. C. output of the power pack is grounded,as indicated at I I6. The potentiometer resistor I is connected to lir90, which is grounded at I I8.

Referring again to the thermionic amplifier 92, it will be observed thatpositive potential is applied to the plate 90 from potentiometerresistor I05 by means of lead i03 connected to adjustable tap I04. Thecathode 93 is connected through line II9, resistor I20 and line I2I tothe cathode 93. From an intermediate tap I23 on resistor I20, there isconnected a resistor I28 which is in turn connected to the photoelectriccell lead M at I2'I. To the junction of line H9 and resistor I20, thereis connected an intermediate resistor I29 which is connected by means ofline I30 to the cathode I4I of a thermionic amplifier, generallydesignated I40, and by means of line I3I to tap I32 on a potentiometerresistor I05. One terminal-of each photocell is connected to ground Theenergized photocell-grid connection 9I is connected to terminal I22 ofthe cam operated switch, generally designated 99, the

other terminal I25 of said switch being connected by line I28 tointermediate tap I35 on resistor I29. The switch 99 is preferably of themicro type, capable of circuit closure upon operation of a fewthousandths of an inch of travel of roller I28a. As illustrated, switchplate I24 is spring biased into circuit closing relation againstcontacts I24 and I25, but is movable to open circuit condition when camI33 pushes against roller I28a. The switch 99 is preferably mounted onthe machine frame and cam I33 on a reciprocating machine part such as,for example, the vertically reciprocating tool carrying head of thepress. i

The cathode lead I2I of the thermionic amplifier 92 is connected bymeans of lead I34 to the grid control I42 of the amplifier I40. The

cathode I4I of amplifier I40 is indirectly heated ass 3,313

by filament I43, energized from an alternating current source, and theentire tube I40 is shielded as indicated at I46, the latter beinggrounded at I41. A screen grid I44 of the amplifier I40 is connected bymeans of line I50 to tap 'I5I onpotentiometer resistor I05 andthe plateI45 is connected by means of line I52,toa relay I53 which is preferablyof the telephonetype, and thence through line I54, milliammeter I55 andline I56 to the maximum voltage tap I5I of the potentiometer resistorI05. A condenser I58 is preferably connected across the relay I53.

The telephone type relay I53 is provided with two make and breakcontacts I53--A and I53B,

which are effective. in the machine control circuits as hereinafterdescribed. As shown in Figure 3, the contacts I58-A and I53-B are in theposition which they assume when the coil of relay I53 is energized, thiscondition being obtained when the photocells 89-69 are both dark or whenthe cam switch is not being held in open position by the cam. When thecoil of re1ay-l53 is dc-energized, contacts I53A and I53--B move to thedotted line positions shown in Figure 3.

The machine control circuits for eilecting starting and stopping of thepress includes the clutch. operating motor element having solenoid 230,the movable core 23I which actuates a lever 234 pivoted at 235. Thesolenoid is retracted by weight or spring 233. During normal running ofthe press, the solenoid is energized as shown in Figure 3, due to theclosure of both contacts I80B and I60--C.

The control of solenoid 230 is controlled by a relay I60, which operatescontacts I60--A and the previously mentioned contacts I60-B and I60C inthe circuit of solenoid 230.

A switch I59 may optionally be included and is for the mechanicaldetection of physical deviations in the material or dimensions of thework parts undergoing processing. This switch is of anysuitable'mechanically operated type having a normal condition shown infull lines of Figure 3. When deviations in the material or dimensionsoccur, the movable element I of switch I59 assumes the dotted lineposition. The mechanical detection switch may optionally be used inconjunction with the photoelectric inspection device for controlling theoperation of the press. Where not used,,lead I64 is connected to leadI68 and lead I83 is omitted.

A lamp relay H0 is provided so that the press will be stopped in theevent any of the lamp bulbs 55 or 55 burn out during service. Oneterminal of each of the lamps 55 and 55 is connected to line I85 whichextends to one terminal of a suitable low voltagev alternating currenttransformer I89. The other terminal of each of the lamps 55 and 55' isconnected to line I86 leading to one terminal of the winding relay I10,the other terminal of the winding being connected by line I88 to otherterminal of the low voltage winding of transformer I89. The primary oftransformer I89 is connected directly to lines H0 and III and isenergized continuously when switches I09--I09 are closed. The relay I10is biased 'to the open circuit position by means of spring I90 and isadjusted so that the decrease I 2,888,;13 a screen or window that ispulled down in front of the machine for the protection ofuthe operatorduring the automatic operation of the machine. The screen or window maybe utilized to operate switch 2I5, with the result that when the screenor window is in a position so as .to protect the operator, a movableelement 2I1 of the switch is in contact with terminal 2I2, and whenthewindow is moved out of the way so as to allow adjustmentsof the machine,the switch blade 2I1 will be moved to the dotted line position (Figure3).

The terminal 2I6 of the window switch 2I5. is connected byline 2| 9 toterminal 220 which but upon de-energization of the telephone-relay I53,contact I53-B drops into contact with terminal 220.

Operation It may be assumed that the mechanical power supply of thepress is operating but that the conventional clutch is disengaged andthe press is at a standstill. In order to place the press and theprotection system in operation, switches I09-I09 are closed therebyenergizing the alternating current supply lines lI-III.. Switch H3 isalso closed thereby energizing the amplitier power pack I06.

The energization of lines Il0-III is conveniently indicated by a pilotlamp 236, which is connected through lines 231 and 238 respectively, tothe alternating current supply lines H0 and I II. Energization of supplylines H0 and III applies power to the primary of transformer I89. lamps55 and 55' and consequently energizes lamp relay I 10. The energizationof relay I10 establishes a circuit between stationary contacts I69 and"I. It is assumed that the mechanical detector switch I59 (if used) isin the position shown in Figure 3, viz: establishing a circuit withstationary contact I66, and that the movable contact 2I1 of window orscreen switch 2I5 is l in engagement with stationary contact 2I2likewise as indicated in Figure 3. It is likewise as- .sumed that a workpart is in proper position as shown in Figure 2 and photocells 69 and69' are hence not illuminated. I

The closure of switch I I3 supplies alternating current power to thepower pack H6 and thus serves to energize the potentiometer resistorI05. This in turn serves asa direct current power source for theamplifier portion'oi the system shown in the upper part oi Figure 3, andthe amplifier is placed in operation.

During normal operation, with the photocells dark, current is' passed inthe cathode anode circuits of both amplifying tubes 92 and I40 and therelay I53 is therefore energize'd. As a result, the contacts I53-A andI53--B of the relay I 53 are in the raised position, viz: contact I 53-Ais in engagement with stationary contact I14 and contact I53--B is inengagement with stationary contact 22I. Relay I53 is very fast acting,and may conveniently be a telephone.

type relay with two pairs of make and break contacts, normally biased tomake with one of each of the sets" of contacts and capable, whenenergized. of making with the other of each 01 the sets of contacts. Solong as the clutch solenoid 230 is de-energized, the press does notopgrounded alternating current line I.

is in the lower position. In order to initiate operation of the machine,push-button 2I0-is momentarily pressed, thus establishing a circuit fromalternating current source IIO through line I6I, the coil of relay I60,line I62, junction I63,

line 209, acrqss push button contacts 208206, Y

line 205, across contacts 2I2 and 2I1 of switch 2I5 and thence togrounded line III. "It will be noted that the starting circuit justtraced, by-' passes all of the safety and protection controls and byholding in the start button, 2I0, the press may be caused to operate afew cycles to ifeed in parts.

Once the relay I60 is energized by pushing the start button 2I0, itestablishes a work circuit through the clutch solenoid 230throughcontacts I60-B and I60-C, and also'causes the establishment of aself-holding circuit by operation of its contact I60-A. r

The circuit of clutch solenoid 230, so established, extends fromalternating current power source II 0, through line 226, contacts223-224 which are bridged by contact I60-B, thence through line I21- tothe winding of clutch solenoid 230, line 229 to contact 221, and thenceover movable contact I60-C of relay I 60 to stationary contact 228 andthen through line 229 to the The clutch solenoid 230- accordinglyoperates and lifts solenoid core 23I upwardly against the action ofspring or weight 233 and the machine begins to operate. The self-holdingcircuit for relay I60 is established from relay I60, junction I63,through line I 64, and the movable contact I65 of the mechanicaldetector switch to contact I66 of said switch, thence through line I68,

This causes the illumination of terminal I69 of relay I10, across themovable contact of relay I 10 and contact In through line I12 throughmovable contact I5 3A- or the telephone relay I53 to contact I14,through. lines I91 and 200 to contacts 20I and 202 which are I601 thencethrough line 203 to line 205, and contacts 2I2 and 2I1 oi the safetyswitch 2I5, to grounded alternating current line III. The machine isaccordingly in operation.

As previously explained, the reciprocating work forming operation of thepress serves periodically to open the cam switch 99 through the actionof cam I33 upon the roller I28.

condition to serve," efiectively to inspect and guard the work, and areefiective to stop the operation of the machine in the event a work partis deranged sufliciently to allow light from either of the lamp sources5555' to impinge upon photocells 69--69' respectively. When switch 99 isclosed, as occurs when cam I33 is out of engagement with the roller 228of switch 99, the action of the photoelectric inspecting device isobviated, this non-function period being allowed during the actualworking portions of the cycle and during such portions of the "worktransferring movement as to cause the work parts normally to be out ofalignment with light beams A. This functioning and non-functioningeffect of the photocell and amplifier circuits is accomplished asfollows:

Assume that the photocells 69-69 are dark and switch 99 is depressed(open). With the cathode 93 of amplifier tube 92 heated, the tube isconductive and current flows to the positive tap I04 (of potentiometerresistor I05) through line I 03, plate 96, cathode 93, line I 2I,resistor eratedue to the fact that solenoid plunger 23I Whenever theswitch 99 is opened, the photocells 69-69 are in the clutch solenoid 230is de-energized and the being dark),asteadypotentialexists at tap I23 onresistor I20, this potential beiiig more -p'ositive than groundpotential due to the resistance drop through the portion of the resistorI20 between tap I23 and grounded line II 91 Resistor I26 is of highohmic value but due to the fact that switch 99 is open and thephotoelectric cells are at a low level of emissivity (due to the factthat they are'dark) the positive potential of tap I23 (on resistor I20)is communicated to the grid- II of the screen gridv I44 of tube I40 isadjustable and the potential of cathode MI is likewise adjustablethrough tap I3'2, the conductivity of tube Y I40 may thus beconveniently adjusted so as to cause telephone relay I53 to remainoperated undersuch steady (photocell dark) conditions.

When either of the photocells 69 or 69 (or any other photocell 69"whichmay be used in the inspection system) becomes illuminated whileswitch 99 is open, the conductivity of the photocell increases, viz: theresistance decreases and.

allows the positive potential on grid line 9| to be dissipated to groundthrough the illuminated v photocell. The resistance I26 is ofsufficiently high value that it is unable to replenish the charge online 9I so long as the photocell remains illuminated, and there is aconsequent reduction in potential of line 9|. Thermionic tube 92 thencore 23I moves under the influence of the weight orspring 233 and causesthe clutch of the mathereby bringing the press to rest.

The press may however coast a slight distance and this may be sufficientto cause m I33 to move out of engagement with the roller I28 thus'allowing switch 99 to close. Since the relay I60 and relay 230 arerelatively slow acting, theinstantaneous de-energization of relay I53would ordinarily not allow sufficient time for relays I50 and 230 tooperate. The re-closure of cam switch 99 would thus serve .tore-establish normal operation, even though relay I53 had de-energizedduring the inspection period and would obviate the effect of thephotoelectric'protection system. In order to prevent the telephone relayI53 from again being energized with consequent false establishment ofnormal operation, there are provided relay contacts I53-B. When therelay I53 is de-energized, contact I 53-B moves into chine to. bedis+engaged from its power source engagement with contact 220, and theground potential, which was normally applied through line |9I upon tapI92, is removed. This in effect inserts additional resistance in thepotentiometer resistor I05, the inserted resistance being between tapI92 and grounded line 90. This causes a sufficient change in thevoltages of taps I 32 and I5I to shift the thermionic amplifier tube Ito non-conductive condition and causes the telephone relay I53 to remainin de-energized condition regardless of the position of cam I33 inrespect. to switch 99.

The machine being thus stopped and the operator raises the window orguard in front of the machine, consequently. the movable contact ofwindow switch 2 I1 is moved out of engagement becomes less conductive.As a consequence, the

from grounded lines 90 (and 9) through resistorJ 20 to line I 21, iscaused to decrease with consequent reduction in the positive potentialat tap I23 on resistor I20. Inasmuch as resistor I26 is fed from tapI23, there' is uneven lesser tendency for the voltage of the grid line9I to be replenished as the conductivity of tube 92 decreases and theeffect is thus differentially cumulative. Once the photocell becomesdarkened and tube 92 starts to become less conductive, its initialresponse in the direction of decreasing conductivity in effect helps todecrease the potential of the grid 9| and hence helps still further todecrease the conductivity of the tube 92. In this manner, extremesensitivity is achieved with small photocells and relatively low candlepower lightbeams.

As the conductivity of' tube 92 decreases, the

potential on line I34 becomes less positive and consequently reduces thenormal positive potential on'grid I42 of tube I40. This causes tube I40with contact 2I2 and into engagement with contact 2 I6. This establishesa grounding circuit for.

' 2 I1 and stationary contact 2I6 of the switch H5,

line 2I9, contact 220 and the movable contact I53 -B of thetelephonerelay I53 (which is then de-energized), through line I9I to tap I92.This re-establishes the normal ground at .tap I92, and

the voltage gradient along potentiometer resistor I05 resumes a normalcondition. When the deranged work parts are again placed in properposition to interrupt the light impinging upon the I transferred bymeans of the transfer bars 20, and

the photocells.

to become less conductive and relay I53, which I has been energized;drops out and allows contact I53 A to move-fromcontapt I14 to'con'tactI11,

and contact I53B to move from contact 22I to' contact 220 -The initialoperation of relay I53 may be very rapid, but contact I53-B serves, ashereinafter explained, to maintain relay I53 deenergized, no matter howshort the duration of the initial drop-out period may be.

The movement of contact I53-A serves to interrupt the self-holdingcircuit of relay I60 and it therefore drops out, causing contacts 204,I60-A, 50-3 and I60-C to interrupt the circuits they had beenmaintaining. Consequently,

this normally allows flickering light to fallupon However, cam I33 is ofsuch a length and is so positionedas to allow only short normally bedark due to the light interruption caused by properly positioned workparts. The inspection periods are thus determined'by the inspectionperio'ds (i. e. ,opening ofswitch 99$" and during such times as thephotocells should length of cam I33. During the remaining non- I22 (ofswitch, 99) to linell.

potentiometer resistor i relay I53,

' conductivity. of the photoelectric cells 69-69" when they areilluminated, but when switch 99 is closed, a circuit is established fromtap I35 on resistor I29through line I28, contacts l25, I24,

tap I35 is approximately the same positive potential as normallyprevails at tap I23 of-resistor I20 during the periods the photocells69-69 are darkl However, the power supplied through the resistor I29(via switch 99 when closed) is comparatively much greater than isavailable through the high resistance I26 and is 'suiflcient tomaintainthe voltage of the photocell-grid line 9| at its normal positivelevel even though one or all of the photocells 6969f .becomeilluminated. Thus by simple closure of the The potential of switch 99,the voltage of line 9I is maintained and accordingly the falling oflight upon the photocells is ineffective to stop the press.

Th operation of mechanical detector switch I I59 is efi'ective to causestopping of the normally operated machine by breaking the circuit ofrelay I60 which is normally maintained through the movable contact I65of switch I59 and stationary contact I66. When this occurs, relay I60 isdeenergized and the machine stops. When the contact I65 engages contactI61, a, circuit is established from line IIO, lin I6I. coil of relayI60, line. I62, junction I63, line I64 through the movable contact ofswitch I65, stationary contact I61, line I63, line I19 throughindicator-lamp I80 and line I8l to alternating current line III.

.In the event either of the lamps 55 or 55' burn out, the lamp relay I10becomes de-energized and breaks the circuit from contact I69 to "I. Thiscauses the de-en'ergization of the holding'circuit of relay I60 andconsequent stoppage of the machine.

Since the thermionic amplifiers 92 and I40 are normally in aconductivecondition, any disablement of these thermionic tubes which decreasestheir conductivity will cause stoppage of the machine due to thedropping out of the relay I53. Thus, should filament 94 of tube 92 orthe filament I43 of tube I40 burn out, this automatically causes astoppage of the machine by de-energization of relay I53. When theoperator of the machine discovers that no work; part is de-ranged, he isimmediately informed that.

the stoppage is due to causative factors other than disarranged workparts. Similarly, any failure of the power pack I06 likewise causes aninterruption of direct current supply to the I05 and this likewisecauses the dropping out of relay I53 and consequent stoppage of themachine.

In the event of normal'stoppage, or stoppage I due to failure of theamplifiers 92-94, telephone power pack I06 or photocell illuminatinglamps 55-55, the machine may be started for operation without benefit ofthe inspection device until servicing is available, by closure of theby-pass switch I95, which allows a circuit to be established fromalternating current supply line I I0 through line I 6|, coil of relayI60, line I62, .junction I63, line I64, movable contact I65 andstationary contact I66 of the mechanical detector switch, line I68, lineI93, contact I96, by-pass switch I95, lines I91 and 200 through thecontacts MI, 202 and I-A (of relay I60),

line 205, contacts 2I2 and 2 of theswitch 2| 5 to alternating; currentsupply line III. The holding circuit-of relay I60 may thus be estab--lished and themachine operates until service on the inspection andprotection apparatus is available. The machine, is of course, re-startedby momentary closure of the starting switch 2I0 after any interruptionmWhen the stoppage'ofwthe machine is due to the normal guardingfunctioning of the photoelectric cells and consequent operation of relayI53, a circuit is maintained through indicator I lamp I 80 as follows:

From alternating current line IIO, line I6I, relay I60, line I62,junction I63, line I64 through switch I59, line I68 through the closedcontacts of a typethat is brought periodically into contact with thework, the movable element I65 may momentarily, be shifted from contactI66 to contact I61 piece which is mechanically irregular. By adjustmentof the spacing of contacts I66 and I61, such momentary interruptions maybe made insufficiently small so as to be shorter than the dropout timeof relay I60. As a consequence, for each cycle of operation of thepressduring suchmechanical defect passes, the lamp I80 is flashed, I'heoperator may then stop the machine normally by opening the supply lineswitches I09-I09, or raising'the window with consequent opening of thecircuit of relay I60 at switch 2I5. Where the duration of opening of themechanical detector switch I59 is sufliciently long to allow relay I60to drop out, this will cause stoppage of the machine and the lighting oflamp I00.

Referring to Figures 5, 6 and 7, there is illustrated a modified form ofcam for operating switch, generally designated 99. The frame of the cammounting is generally designated 250, and is shaped at, 25I and formedwith apertures 252 and slots 253-254 so as to allow convenient mountingon the machine and adjustment in the horizontal direction as shown inFigure 5. The frame 250 has a slot milled in it at 251 shown in Figure7, Bifurcated ends- 259 and 260 receive a rocka'ble cam plate, generallydesignated 265, which'is provided with a bushing 266 and pivoted uponthe pin 261 passing through the bifurcated ends. The cam plate 265 issymmetrical about its pivot axis and has opposite identical cam surfaces268 and 210 which are curved up at the ends 269 and MI respectively. Atthe mid-back portion, there is a central tip 213 against which a detentball 214 is adapted tobe pressed by means of a spring 215. spring 215may be adjusted by means of screw 211, which is threaded intoa hole 218drilled in the body of the frame 250; The adjustment screw 211 is inturn adapted to be heid in .ad-

is insuificient to cause the actuation and back again for each work.

- the up stroke.

reciprocating part, and the switch on a stationary part, although thecam may be mounted upon a stationary part of the machine and the switch99 thereby is mounted upon the moving part. Thus,.when the plate 250ismoving vertically downward in the direction of arrow 285, the leadingedge of the cam, i. e. the center portion 288 abuts against the rollerand forces it in the switch closing position shown in Figure 5. Theroller I28 is pressed backward from the dotted position I28 by theportion 210 of the cam adjacent the middle 288. The roller then rollsalong the then nearly vertical part 268 until the portion 269 of the camcomes abruptly intocontact with the roller I28 When this occurs, theresistance of the roller I28, which is spring pressed to the left asshown in Figure 5, by an internal spring (not illustrated), causes asufficient force to be placed upon the ball detent 214 by means of thetip 213 so as to force the ball backwardly against spring 218 whereuponthe cam 265 is rocked upon its pivot 261 into the position shown inFigure 6, in which it stays until the press part moves in the verticallyupward direction illustrated by arrow 290 in the roller whereuponsuflicient force is again placediiponj the rocking cam 268 to overcome alow resistance feed circuit connecting'said grid and a said source ofpositive potential, and

means for interrupting said low resistance feed circuit when theworkshould normally be at said inspection station.

2. An apparatus of the type set forth in claim 1 further characterizedin that means is provided for working the parts at a work station andforv potential having its positive side connected to said the'rsistanceof the spring pressed detent ball" 214 and the cam plateis snapped tothe position shown in Figure'5.

The merit of the snap action cam andswitch arrangement illustrated inFigures 5, 6"an'd '7 resides in the fact" that slight variations intiming of the inspection period may thus be provided with reference to adatum point on corresponding reciprocating parts of the press. Thus,referring to pins I94 (Figure 4), it will be observed that theinspection period on the down stroke of the press head, indicated by thebracket 13, occurs at a somewhat lower position of the press head thandoes the inspection period 80 of This functioning is of especial meritso as to allowdziming. of the inspection period to occur during periodsof the press operation when stopping ,isn iost favorable.

Many obvious variationswvill be apparent to those skilled in theart andsuchare intended illustrated,

to be within purview of'the'invention described andclaimed'. j We claimas our invention:

l. A. photoelectric inspection apparatus for work parts that areperiodically moved-into a work plate and its negative side connected tothe oathode, a high resistance feed circuit connecting the said grid anda voltage supply having an intermediate value relative to the negativeand positive sides of said' source, said photocell being connectedbetween the grid and negative side of said source, a low resistance feedcircuit connected to said grid and to another voltage supply ofintermediate value relative to the negative and positive sides of saidsource, and witch means for periodically opening said low resistancefeed circuit.

4. In an apparatus for working parts successively having a reciprocatingworking means and means on said apparatus for moving parts to and from aposition to be worked upon by said working means, means for interruptingthe operation of said working means when a work part is not in positionto be worked comprising a light source mally assumed by said work partbefore being workedfupon, a; photocell positioned to collect light notintercepted by a work part in said position, a

thermionic amplifier for said photocelL-havinga cathode, grid and plate,a source of. direct current potential having its negative connected tosaid I cathode and positive connected to said plate, said photocellbeingconnectedto said grid and said. negative, a highresistan'ce feed circuitconnected to the grid and a source of positive potential, a lowresistance feed circuit connecting said grid f and a source of similarpositive potential, and

means operated synchronously with said working means'for interruptingsaid low resistance feed circuit except for a short period precedingworking of said part.

5. In an apparatus for working parts successively,'having areciprocating working means and m eahs,on said apparatus for movingparts to and. from a position to be worked upon by said working; -means;means for-interrupting the operation of said working means'when awork-part is not in position tobeworkedcomprising alight sourceinspection station comprising means forfocus? ing a light beam acrosssaid work inspection station in a position to shine upon work parts inposition at the station, a photocell positioned to collect light notintercepted by said work parts, a thermionic amplifier for saidphotocell having a cathode, grid and plate, a source of direct currentpotential having its negative side connected to said cathode andpositive side connected to said plate, said photocell being connected tosaid grid and negative side of the direct current source, a highresistance feed circuit connecting the grid and a source of positivepotential which is positive in respect to the negative side of saidsource of direct current potential,

fo focusingp beam of light upon a position nor: mally assumed bysaid-work part beforebeingworked upon, a photocell positioned to collectlight not intercepted by a workpart in said position, a thermionicamplifier for said photocell, having 'a cathode, grid and plate, a'source of direct current potential having its .negative connected tosaid cathode and positive connected to said plate, said photocell beingconnected to said grid and said negative, a high resistance feed circuitconnected to the grid and 'a source of positive potential, a lowresistance feed circuit connecting said grid and a source of similarpositive potential, and means operated synchronously with said workingmeans for interrupting said low resistance feed circuit except for ashort period preceding and succeeding working or said part.

6. A photocell amplifier comprising a grid controlled thermionic tube, ahigh resistance circuit connecting said grid and a first supply of,electrical potential for supplying a limited flow of electrical energyto said grid, photocell connecting trolled thermionic tube having aplate and cathode, a unidirectional source of plate potential having itspositive side connected to said plate, a resistor having an intermediatetap, said resistor being connected from the negative side of said sourceto said cathode, a high resistance circuit connecting said intermediatetap of the resistor and said grid and a photocell connecting the gridand negative side of said source.

8. The apparatus of claim 6 further characterized in that a lowresistance connector having a control switch therein is provided betweensaid grid and said source of electrical potential which is positive inrespect to said second supply.

9. A photoelectric inspection apparatus for work parts that areperiodically moved into a work inspection station comprising meansforfocusing a light beam across said work inspection station in aposition to shine. upon work parts in position at the station, aphotocell positioned to collect light not intercepted by said workparts, a thermionic amplifier for said photocell having a cathode, gridand plate, a direct current. source of plate potential having itspositive side connected to said plate and negative connected through apotentiometer resistor to said cathode, said photocell being connectedto the grid of said tube and to the negative side of said source ofpotential, a high resistance feed circuit for establishing apredetermined potential on said grid when the photocell is notcollecting light, and a low resistance feed circuit for maintaining saidpotential on the grid when the photocell collects light dursaid parallelcircuit when said work parts are normally in a position to be inspected.

v 11. In a reciprocating metal working machine wherein the work is fedinto the machine worked upon and ejected as a cycleof operation, animproved control mechanism comprislhg a photoelectric inspectionapparatus including means for projecting alight beam on the work fedinto the machine and photocell means responsive thereto for determiningproper positioning of the work during said cycle and during a timeperiod prior to and afterbeing worked upon and a switch means forinactivating the inspection apparatus except for a predeterminedinterval before and except for another predetermined interval afterbeing worked upon.

12. In a reciprocating metal working machine wherein the work is fedinto the machine worked upon and ejected as a cycle of operation, animproved control mechanism comprising a photoelectric inspectionapparatus including means. for

ing normal movement of parts into and out of inspection position.

10. A photoelectric inspection apparatus for work parts movedperiodically through normal positionsa light source P sitioned to directlight against said work parts, a photocell positioned to collect saidlight when the light is not intercepted by a work part being inspected,an amplifier tube having a cathode, grid and plate, a source of directcurrent potential, the positive side of said source being connected tothe plate of the amplifier tube and the negative side being connectedthrough a resistor to the cathode of said tube, the grid of said tubebeing connected to a source 'of potential having a value intermediatethe potentials of said positive and negative sides said photocell beingconnected from said grid to the negative power source,'and a parallelcircuit connecting said grid and a source of potential having a value,relative to said negative and positive sides,

not substantially less positive than the potential at which the grid ismaintained when the photocell is dark, and means for periodicallyopening projecting a light beam on the work led into the machine andphotocell means responsive thereto for determining proper positioning ofthe work during said cycle and during time periods prior to being workedupon, and a switch means for inactivating the inspection apparatusexcept durin said time periods. l

13. The apparatus of claim 11 further characterized in that saidinspection apparatus is inactivated by a cam operated switch which isclosed cyclically by the machine tor a short period preceding and ashort period after the work operation.

14. The apparatus of claim 11 further characterized in that saidinspection apparatus is inactivated by a cam operated switch which isclosed cyclically by the machine or a short period preceding and a shortperiod after the work operation,.said cam being movable slightly to varythe cyclic timing. 15. In an inspection apparatus for a metal workingmachine having a frame and a metal working tool movable in cyclicreciprocating relation with respect to the frame, a photoelectricinspection device including switch means for disabling the inspectiondevicefduring a portion of each reciprocating cyclic work motion of saidmetal working machine, said switch means being cam operated by areciprocating member of the machine, the cam being shaped so as topresent an identical pattern on each side oi a pivot point, a pivotsupport for said cam at said pivot point, and stop means for holding thecam in limited pivoted condition for presenting to said switch means anidentical switch operating cam suriace beginning at a limited range mthe movement or said reciprocating member.

16. The apparatus of claim 15 further characterlzed in that the'can'ioperated switch is a miinitial motion or an operating member which is 1thereafter movable through an additional dissaid parts comprising lightsources at each of a plurality of said stations for projecting lightagainst the space assumed by ,a properly positioned part undergoingworking, a photocell for each station positioned to intercept light thatis not intercepted by a. work part, 8. thermionic amplifier having acathode, grid and anode,'mea.ns having a. positive potential relative toground potential and connected to the grid for electrically chargingsaid grid at a limited rate, said photocells being electricallyconnected to the grid and to groundfor discharging the grid when lightfalls upon a cell, the rate of charging of said grid being sufiicientlylow to allow substantial discharge by a. photocell when the latter isilluminated, and a, second means connected to said grid and to a. sourceof supply which is positive in respect to ground for charging the gridat a rate beyond the capacity of the cells to'discharge it even whenilluminated.

HARRY WILLIAM HOFFMAN. GROVER H. HELMER.

